It was whilst Augustus was spending the winter of 1792 in Rome that he met and fell in love with Augusta Murray, daughter of John Murray, 4th Earl of Dunmore. They were soon married in a ceremony conducted by a Church of England clergyman named Gunn at the Hotel Sarmiento on the 4th April 1793, but in order to avoid any doubt on the matter they returned to England and repeated the exercise at a clandestine ceremony conducted at St. George's in Hanover Square, London on the 5th December that same year.

The clandestine nature of their marriage was occasioned by the knowledge that king George III would not have approved of it, unfortunately the secret was not kept for very long, as the birth of a son on the 13th January 1794 soon brought the matter to the attention of the king. The marriage was formally annulled on the 14th July 1794 by the Court of Arches in accordance with the Royal Marriages Act 1772. Augustus however, simply ignored this decision for many years and continued to cohabit with Augusta. It was not until after the birth of their second child, a daughter in 1801, that they finally separated and abandoned their partnership.

Although Augustus had been appointed to the Order of the Garter on the 2nd June 1786 he had not been awarded any further dignities on coming of age and had to be content with being plain 'HRH Prince Augustus KG'. It was not until he'd agreed to dump Augusta that he was finally awarded the titles of Baron Arklow, Earl of Inverness and Duke of Sussex on the 27th November 1801. As it happens his father had a number of reasons to be disatisfied with Augustus other than his taste in women. For one thing Augustus was something of a liberal, a tendency that he had apparently developed at an early age, having been once punished at the age of seven for wearing Admiral Keppel's election colours. (Admiral Augustus Keppel was regarded as particularly dangerous Whig by the king.) Indeed Augustus was later to favour all the popular progressive cause celebres of his time, and openly supported such things as parliamentary reform, the abolition of the slave trade, the repeal of the corn laws, and the removal of civil disabilities for Roman Catholics, Dissenters and Jews.

These were of course dangerously radical ideas, but then Augustus was something of a genuine intellectual and unlike his brothers had no taste for matters military and so, to the disappointment of his father did not pursue a career in either the Royal Navy or the army as was expected of him. He was far more interested in his books and amassed a library of 50,000 volumes including no less than 1,000 separate editions of the Bible and was known to have something of a taste for Biblical studies and collected ancient Hebrew manuscripts. He also displayed a real interest in the arts and sciences and was president of the Society of Arts from 1816 until his death, and also president of the Royal Society from 1830 to 1838. It was reported that he only resigned from the latter post because the entertainment expenses forced on him in his capacity as chairman ate into his book buying fund.

In later life and after the death of his first 'wife' in 1830 Augustus married once more. Or at least sometime in early May 1831 he eloped with a Cecilia Letitia Underwood, daughter of Arthur Saunders Gore, 2nd Earl of Arran of the Arran Islands and widow of Sir George Buggin. As it happens this second marriage was also in contravention of the Royal Marriages Act 1772, but by then George III was dead, Augustus was fifty-six and no one minded very much. Although his partner was thus not considered as having the right to call herself the Duchess of Sussex, Augustus's elder brother William by then king, granted Cecilia her own title as Duchess of Inverness in 1840.

Augustus lived out the remainder of his life quietly enough, content with his books and the attentions of the Duchess of Inverness. His niece, Victoria was later to remember that her parents would threaten her with punishment by 'uncle Sussex' should she misbehave and so grew up in fear of the Duke. But she appears to have conquered her fears in later life as it was Ausgustus who gave her away at her wedding to Albert of Saxe-Coburg-Gotha on the 10th February 1840.

Augustus eventually died at Kensington Palace from erysipelas on the 21st April 1843. He was buried in the public cemetery at Kensal Green rather than at Windsor with the rest of his family in accordance with the instructions set out in his will.

There were two children born of his first marriage who both took the name of d'Este. There was a son named Augustus Frederick d'Este born in 1794 who became a colonel in the British army. After his father's death in 1843 he put forward a claim to the Sussex dukedom and his father's other titles which was denied by the House of Lords. He died unmarried in 1848. His younger sister, Augusta Emma d'Este, born 1801 married Sir Thomas Wilde, 1st Baron Truro of Bowes. The Duke is also known to have had at least one other illegitimate daughter, a Lucy Beaufoy Tranter whose mother is identified only as a 'Miss Tranter'.

Augustus was also a keen freemason, as indeed were almost all of his brothers. Initiated into the craft at Berlin in 1798, in 1813 he followed his brother George (then Prince Regent, later George IV) as Grand Master. As it happens, his brother Edward, Duke of Kent was Grand Master of the rival order of Ancient or Athol Masons, and it was largely due to the efforts of the two brothers that the two orders merged. Augustus therefore became the first grandmaster of the United Grand Lodge of England and after his death was commemorated by a six-ton statue produced by Edward Hodges Bailey in 1846 which now stands in the Sussex corridor of the Freemasons Hall at Great Queen Street in London.

His impressive collection of books, known as the Bibliotheca Sussexiana, "the Extensive and Valuable Library of His Royal Highness the late Duke Of Sussex, K.G" was sold by auction in 1844 after his death by Messrs. Evans of No. 93 Pall Mal.

SOURCES

The entry in The Dictionary of National Biography by Thomas Finlayson Henderson

THE DUKE OF SUSSEX LODGE NO 3343
http://www.loveandcharity6224.org/history3.htm

The Prince Regent and His Circle
http://www.channel4.com/history/microsites/H/history/n-/princeregent01.html